Redarc - To fuse or not to fuse?

Submitted: Saturday, Jun 13, 2009 at 08:33
ThreadID: 69766 Views:8993 Replies:6 FollowUps:16
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Hi, I've done a few searches and can't really find an answer to my question.
I am installing a dual battery system using a Redarc Isolator. The batteries are both in the engine bay, right next to each other. The maximum length of power cablee tto the Redarc is 400mm. I am using 3 gauge (26mm square) cable. The auxillary battery is only used for a fridge, lights etc. I don't have a winch.

My question is: should I put fuses between the isolator and starting and auxillary batteries, or will it be OK without fuses?

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Reply By:- Saturday, Jun 13, 2009 at 08:55

Saturday, Jun 13, 2009 at 08:55
In my opinion Yes.
I used a redarc isolator when I installed my auxiliary battery and I definitely put a fuse onto my auxiliary battery positive lead, very close the the battery terminal.

I also put fuses on every wire I ran from the auxiliary battery just to be safe. In fact I put in a 8 fuse, fuse box through which all my auxiliary power runs. There are no unfused wires.
WBS
AnswerID: 369767

Follow Up By: Bob of KAOS - Saturday, Jun 13, 2009 at 09:43

Saturday, Jun 13, 2009 at 09:43
I agree.

You have to imagine the worst case scenario. Could the 400 mm lead chafe under extreme off road conditions? Could the lead be shorted in a frontal impact?

If the answer to either is 'yes' then a fire could result.

Bob
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Follow Up By: Tenpounder (SA) - Saturday, Jun 13, 2009 at 09:48

Saturday, Jun 13, 2009 at 09:48
Hi there, WBS. I am NOT arguing against your response, since it seems to make perfect sense.
However, when I installed my own system (about 8 or more years ago now) my auto electrician argued against fuses between the isolator and the aux battery, on the grounds that any connector (such as the connections required to insert a fuse into a circuit) represents a potential source of failure or voltage drop. So what's the trade off between electrical performance and safety precautions, in your opinion?
Incidentally, every output circuit from the aux battery has a fuse, like you suggest. The circuit for the 12v fridge element in the van has both slow acting auto-reset CB rated at 15 amps as well as a 20 amp instantaneous fuse, given the tendency of Electrolux/Dometic fridges to draw inordinate current.
Regards
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Follow Up By: Tenpounder (SA) - Saturday, Jun 13, 2009 at 09:52

Saturday, Jun 13, 2009 at 09:52
Looks like you agree, Bob! Incidentally, what is an OK rating for the fuse between the isolator and the aux battery? and where should it be? (Some have suggested one at each end). In my case, the cable runs from the isolator under the bonnet to the aux batt in the rear of the vehicle, so the chafing short risk is sunstantial - hence my interest in the matter!
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FollowupID: 637192

Follow Up By: Peter_n_Margaret - Saturday, Jun 13, 2009 at 10:23

Saturday, Jun 13, 2009 at 10:23
Chris, the purpose of the fuse is to stop a fire if the cable gets too hot, therefore you need one each end (because current could flow from either battery) and it should be the weakest link in the system, but otherwise as big as possiblebecause you don't want it to pop unless there is a dead short somewhere.
In my case I have a 70mm2 cable from the 200A 2 way Redarc (next to the crank) 9m to the house and have a 200A fuse each end of that cable.

Cheers,
Peter
OA196 Motorhome
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FollowupID: 637198

Follow Up By: Tenpounder (SA) - Saturday, Jun 13, 2009 at 10:32

Saturday, Jun 13, 2009 at 10:32
Thanks, Peter, for that clear and concise answer. I think I had better go shopping!
Regards
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Follow Up By:- Sunday, Jun 14, 2009 at 09:11

Sunday, Jun 14, 2009 at 09:11
Hello Chris,
To answer your question specifically. I am not all that smart with electrics so I chose to go down the "wearing two underpants theory" of better being safe than sorry. I thought that if I fuse everything then that was as safe as I could possibly make it. I did not even consider voltage drop and the use of fuses in the one thought. I was not aware of this point. From Memory I put a 50 amp fuse between the battery and the isolator but don't quote me.

I did consider voltage drop in terms of using the appropriate thickness of wire, lengths of wiring and so on though, so I used recommended cable for my Anderson plug, fridge wiring etc. I put my system in in 2006 and no problems so far.

Tom (WBS)
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Reply By: Member - Kroozer (WA) - Saturday, Jun 13, 2009 at 13:19

Saturday, Jun 13, 2009 at 13:19
I asked this same question about a year ago. I was told that by fusing it you cant then join both batteries with the push button as it will just blow the fuse. It bothered me so much trying to make a decision so i took it to an auto sparkie and let him decide. He didnt fit one, just wrapped all the cables in thick heater hose, as both batteries were side by side. Cant see any dramas with that.
AnswerID: 369797

Follow Up By: _gmd_pps - Saturday, Jun 13, 2009 at 13:29

Saturday, Jun 13, 2009 at 13:29
There is only one situation where this is correct and this is when you have an electric winch and run it from both batteries. But in such a situation I'd rather wire a separate connection (very low gauge with manual switch) and have the other connection fused and controlled by override if you really have to use a Redarc or such. So I call this utter nonsense and in 99% of the cases the electricians just compromise on cost because most clients would not want to pay for the best solution or the electricians just don't know better.
EVERY device and EVERY length of cable need to be protected by fuses.

good luck
gmd
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FollowupID: 637217

Follow Up By: Member - Kroozer (WA) - Saturday, Jun 13, 2009 at 15:51

Saturday, Jun 13, 2009 at 15:51
Is your starter motor cable fused? Thats what i was told to consider.
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Follow Up By: Member - Phil G (SA) - Saturday, Jun 13, 2009 at 20:08

Saturday, Jun 13, 2009 at 20:08
"Is your starter motor cable fused? "

No, because it carries a few hundred amps. And when a fuse develops resistance, the vehicle won't start! Every other cable is covered firstly by fusible link at or near the battery and secondly by a dedicated fuse.

Now look at you starter cable to see what a good manufacturer does to prevent the possibility of short circuit of a fat cable. Great insulation, great connectors all well insulated and routed away from metal. It would be nice if dual battery installers would do the same. The heater hose is a good start!

Cheers
Phil
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FollowupID: 637265

Reply By: Member - Phil G (SA) - Saturday, Jun 13, 2009 at 13:31

Saturday, Jun 13, 2009 at 13:31
Chris,

If you were to use the push button switch option to start a dead battery, then NO, you can't use any short circuit protection.

So I'll assume that you are not fitting the starter option. And my answer is YES, you need short circuit protection. Having witnessed a battery fire under a bonnet 10 years back, its not a pretty sight.

But don't use a fuse because they can easily corrode when placed next to batteries and become the source of frustration. Do what the vehicle manufacturers and the smarter Isolator manufacturers do and use FUSIBLE LINKS.

You can buy the Narva Fusible Link material from Motor Traders in Adelaide. The thickest stuff they have is 14Gauge. To make up the fusible link use 2 lengths of 14Ga for each link and crimp (not solder) a good quality 5/16ths connector at each end. One end will go on the pos terminal, the other end can simply be atached to your cable with a short stainless steel bolt. Surround everything in split conduit.

This is identical to what is supplied by Rotronics for their Isolators. You may be able to buy these links directly from Rotronics. Opposite Lock stock the isolators but don't stock the fusible links individually. And make up a couple of extras to carry as spares.

Cheers
Phil
AnswerID: 369801

Follow Up By: Tenpounder (SA) - Saturday, Jun 13, 2009 at 15:10

Saturday, Jun 13, 2009 at 15:10
Phil
Thanks for the extra info.
Regards
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FollowupID: 637230

Reply By: Von Helga - Saturday, Jun 13, 2009 at 19:20

Saturday, Jun 13, 2009 at 19:20
Don't get me wrong I like this forum however why not simply wire the isolator as per the OEM's diagrams.
AnswerID: 369843

Follow Up By: Tenpounder (SA) - Saturday, Jun 13, 2009 at 19:56

Saturday, Jun 13, 2009 at 19:56
Hi there, Von Helga. Two reasons: one:- not everyone uses a retail kit supplied with what you call an OEM's diagrams(some of us have bought a solenoid and an isolator and made up a circuit. Two: some of us like to make up our own minds whether to strengthen our systems or accept the instructions at face value. (How many people have bought stuff fitted with a cigarette lighter connection, only to find the current is well over the rating of the so-called 'lighter' circuit?)
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FollowupID: 637261

Follow Up By: Member - Phil G (SA) - Saturday, Jun 13, 2009 at 20:00

Saturday, Jun 13, 2009 at 20:00
I know what you're saying. But the OEM instructions do not tell a DIY person how to prevent a short circuit.

If you look at the wiring that Toyota use for the twin cranking batteries on the 100series (no fuses!) - The cable is thickly insulated, there is conduit and tape around it as well. It is routed over the radiator shroud so there is no chance of metal contact. The cable is secured in multiple positions but insulated supports that surround the cable and lift it as well. Both battery terminals have secure fitting plastic covers.

Now compare this with either a professional installation or a DIY one. I've never seen an installation as good as Toyota's. I've seen a heap of "professional installations" and conduit is usually left out, and they haven't heard of terminal covers, and cable ties will fix everything tight against metal!!

Rotronics do it right - they supply fusible links to protect the user!
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FollowupID: 637262

Reply By: Maîneÿ . . .- Sunday, Jun 14, 2009 at 11:52

Sunday, Jun 14, 2009 at 11:52
Redarc recommends their Smart Start should to have a “fuse” on each 'pos' (+) battery cable attached as close as practicable to the battery terminal.

more Smart Start Dual battery installation info

I don't use fuses or fusible links in my Dual Battery System's 32mm² cables because I did the installion and elect to accept all percieved risks.

However, when I'm paid to do the same work I *always* use fuses or resettable circuit breakers at each battery (+) terminal.

In your case, I would suggest that it's not nesesary _ IF _ you have the batteries and also your battery cable *securely attached* and YOU are also prepared to accept the entire risk associated with the installation ??
( that was a question - not a statement )

Maîneÿ . . .
AnswerID: 369900

Reply By: joker.com - Thursday, Jun 18, 2009 at 21:03

Thursday, Jun 18, 2009 at 21:03
Thanks for all the replies fellas.
I decided to go without fuses and use , covered in heat shrink, covered by another layer of corrugated split tube just to be safe.


AnswerID: 370764

Follow Up By: joker.com - Thursday, Jun 18, 2009 at 21:06

Thursday, Jun 18, 2009 at 21:06
This post was supposed to read:
Thanks for all the replies fellas.
I decided to go without fuses and use corrugated split tube conduit, covered in heat shrink, covered by another layer of corrugated split tube just to be safe. No chance of rubbing thru!
Thanks again for the help!

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FollowupID: 638062

Follow Up By: Maîneÿ . . .- Friday, Jun 19, 2009 at 08:44

Friday, Jun 19, 2009 at 08:44
You have fitted the Redarc almost horizontal - not Vertical ??

Maîneÿ . . .
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FollowupID: 638107

Follow Up By: joker.com - Friday, Jun 19, 2009 at 14:04

Friday, Jun 19, 2009 at 14:04
Mainey, I rang the Redarc tech line first to see if it had to be mounted vertically. I was told it can be mounted in any direction EXCEPT upside down.
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FollowupID: 638160

Follow Up By: Maîneÿ . . .- Friday, Jun 19, 2009 at 22:34

Friday, Jun 19, 2009 at 22:34
Did you ask them why they could not be mounted "upside down" ??

I think you will find it's the same reason they should not be installed horizontal

Maîneÿ . . .
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FollowupID: 638278

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